Catheters are tube-like medical instruments that are inserted into a body cavity organ or blood vessel for diagnostic or therapeutic reasons. Medical vascular catheters are particularly designed for insertion into the vasculature and are available for a wide variety of purposes, including diagnosis, interventional therapy, drug delivery, drainage, perfusion, and the like. Medical vascular catheters for each of these purposes can be introduced to numerous target sites within a patient's body by guiding the catheter through an incision made in the patient's skin and a blood vessel and then through the vascular system to the target site.
Medical vascular catheters generally comprise an elongated, flexible catheter tube or body with a catheter side wall enclosing a catheter lumen extending between a catheter body proximal end coupled to a relatively more rigid catheter hub to a catheter body distal end. The catheter body may be relatively straight, or may inherently curve, or may be curved by insertion of a curved stiffening wire or guide wire through the catheter lumen. The catheter body and catheter side wall are typically fabricated and dimensioned to minimize the catheter body outer diameter and side wall thickness, and to maximize the catheter lumen diameter while retaining sufficient side wall flexibility and strength characteristics to enable the catheter to be used for the intended medical purpose.
One of the therapeutic procedures applicable to the present invention is known as percutaneous transluminal coronary angioplasty ("PTCA"). PTCA can be used, for example, to reduce arterial build-up of cholesterol fats or atherosclerotic plaque. Catheters must have sufficient stiffness to be pushed through vessels as well as rigidity to provide a high degree of torsional control. Stiffness or rigidity in the catheter tip poses the danger of puncturing or otherwise damaging a vessel as it twists through the vascular system. It is therefore desirable for catheters to have a soft or flexible distal tip.
Commonly-owned U.S. patent application Ser. No. 09/188,760 filed Nov. 9, 1998 for GUIDING CATHETER AND METHOD OF FABRICATION, in the name of Thierry Benjamin describe various prior art methods of attaching distal soft tips to proximal catheter shafts and their improvements upon those methods.
U.S. patent application Ser. No. 09/046,241 filed Mar. 23, 1998, for CATHETER HAVING EXTRUDED RADIOPAQUE STRIPES EMBEDDED IN SOFT TIP AND METHOD OF FABRICATION, in the names of Nasser Rafiee et al. describes a catheter shaft having a radiopaque stripe(s) co-extruded in the side wall of the catheter shaft. In the co-extrusion process, one or more radiopaque stripes can be formed such that each extends substantially parallel with the axis of the tube and with one another. Alternatively, the shaft can be rotated as the co-extrusion takes place to form one or more spiral stripes of the radiopaque material. A disadvantage of the invention is that making the stripes wide enough to be seen under fluoroscopy makes the shaft stiffer and less flexible.
U.S. Pat. No. 5,045,072 to Castillo et al. for CATHETER HAVING HIGHLY RADIOPAQUE, FLEXIBLE TIP describes a distal tip of plastic formulation containing sufficient radiopaque agent (40-75% by weight) to be substantially more radiopaque and preferably softer than portions of the catheter proximal to the tip. Typically, transition zone 13 is free of tubular reinforcing braid, while catheter body 15 carries such reinforcing braid in its interior, in conventional manner. A disadvantage of the '072 invention is that adding metal to the distal soft tip makes it stiffer, thereby leading to greater trauma in the blood vessels. Another disadvantage of the '072 invention is that of not having a reinforcing braid in the transition zone, thereby compromising torkability and kink resistance.
U.S. Pat. No. 5,234,416 to Macaulay et al. for INTRAVASCULAR CATHETER WITH A NONTRAUMATIC DISTAL TIP describes a braided tubular member formed of a plurality of multifilament strands which are impregnated with a thermoset polymeric resin, the thermoset polymer resin which is incorporated into a distal portion of the braided tubular member. The distal tip has at least two relatively short, tubular elements, including a first (proximal) tubular element which is secured to the distal end of the catheter shaft and a second (distal) tubular element which is secured to the first (proximal) tubular element and which is softer than the first tubular element. The first (proximal) tubular element has a radiopaque filler material incorporated therein, such as bismuth trioxide, in order to make the distal tip fluoroscopicaly observable within a patient. The first and second tubular elements are but joined together by suitable means such as by heat fusing or by a suitable adhesive such as cyanoacrylate-based adhesive, e.g., Loctite.RTM. 405. A disadvantage of the Macaulay et al. guiding catheter is that the braided material terminates prior to the radiopaque area thereby compromising torkability and kink resistance.
Problems encountered in adding radiopaque material to a portion of a catheter include the stiffening of the area with the radiopaque material and the raising of the melt temperature of the area with the radiopaque material, thereby making the melt temperatures incompatible with the surrounding areas, thus making melt bonding to the adjoining areas difficult.
Visualizing the distal tip of a catheter under fluoroscopy is important for proper placement of the tip. The problem presented by stiffening due to radiopaque loading is that stiffening disproportionately increases as the walls of a catheter become thinner. In thin wall catheters therefor, less radiopaque material can be loaded than with catheters with thicker walls, thereby reducing visualization in thin wall catheters. For example, 35-40% by weight of BaSO.sub.4 in a 5 French catheter would not be visible under fluoroscopy. Loading high enough amounts of such radiopaque material sufficient for the visualization of the distal tip, however, makes the distal tip too stiff.
It is an object of the invention to enable the physician to see the catheter distal area under fluoroscopy without compromising the flexibility of the distal soft tip. It is a further object of the invention to have an area which is visible under fluoroscopy yet permits torque transfer and remains kink resistant.